1970 Base Engine / 4-Spd
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Le Mans Master
Joined: Jul 1999
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From: Maryland
1970 Base Engine / 4-Spd
It would appear from Chevy by the Numbers and the 1970 Chevrolet Sales Album that the Base Engine 1970 Corvette got the M-20 transmission and the M-21 was NOT available with the base engine. There is no mention of this in the NCRS TIM&JG, in Prince's book, in Dobbins book (though Don said he found it - what page Don? I can't find it.) :) or the Black Book. The Sales book also has ontario orange and the LS-7 listed - both of which weren't available in '70 so I'm not overly confident in the book as gospel. :lol: Does anyone else have information confirming this? Thanks, ~Juliet
[Modified by Juliet, 12:12 AM 9/19/2002]
[Modified by Juliet, 12:12 AM 9/19/2002]
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Re: 1970 Base Engine / 4-Spd (Juliet)
According to the power team chart on page 50 of the C3 NCRS Spec Guide, the only manual transmission available with the base '70 engine had a first gear ratio of 2.52:1. This would be the "wide ratio" transmission, which was known as M-20. Of course, this wouldn't be on the order form because it was part of the base equipment package, but it would probably be on the build sheet.
If you ordered L-46 or LT-1 the base transmission was the wide ratio, but you could specify the close ratio RPO M-21 (2.20:1 first gear) at no extra cost, and M-21 usually included a different standard axle ratio and a different set of axle ratio options.
NCRS doesn't judge the transmission closely because it is too hard so see any detail with the car on the ground, but a good PV judge should be able to tell which transmission is installed because of the big difference in 3/4 gap between the CR and WR.
Duke
If you ordered L-46 or LT-1 the base transmission was the wide ratio, but you could specify the close ratio RPO M-21 (2.20:1 first gear) at no extra cost, and M-21 usually included a different standard axle ratio and a different set of axle ratio options.
NCRS doesn't judge the transmission closely because it is too hard so see any detail with the car on the ground, but a good PV judge should be able to tell which transmission is installed because of the big difference in 3/4 gap between the CR and WR.
Duke
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From: NM
Re: 1970 Base Engine / 4-Spd (SWCDuke)
...but a good PV judge should be able to tell which transmission is installed because of the big difference in 3/4 gap between the CR and WR.
I don't follow, could you explain?
tom...
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From: Washington Michigan
Re: 1970 Base Engine / 4-Spd (Tom73)
The ratio step from 3rd to 4th in an M-20 (wide-ratio) trans is 1.46:1 to 1:1, and in the M-21 (close-ratio) trans it's 1.28:1 to 1:1; this results in far less rpm drop when shifting from 3rd to 4th with an M-21 than with an M-20. The P.V. (Performance Verification) judging includes a lengthy road test, and a P.V. judge could tell the difference immediately as the owner shifted from 3rd to 4th.
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From: NM
Re: 1970 Base Engine / 4-Spd (JohnZ)
Thanks John,
I knew that, forgot completly about performance verification. Was just thinking in terms of visual inspection and was wondering what three fourths of what. :D :D
tom...
I knew that, forgot completly about performance verification. Was just thinking in terms of visual inspection and was wondering what three fourths of what. :D :D
tom...
